Coating apparatus and method

ABSTRACT

A component such as a door is coated by immersion in a fluidized bed. The component is supported by a hook assembly that moves the component within the fluidized bed during coating. The movement is cyclical and inhibits bridging of the coating material when applied to intricate articles.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.13/744,256, now abandoned, filed on Jan. 17, 2013, which claims priorityfrom U.S. Provisional Application No. 61/587,605 filed on Jan. 17, 2012,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for applying acoating to a component.

Most fabricated articles require a coating to be applied to protect themagainst the environment in which they will operate. One of the mostdemanding environments is salt water, as encountered on seagoingvessels, in which mechanisms and components must be protected again thecorrosive effects of the salt carried in the sea water. The maintenanceof the components is an expensive and continuous process. Painting orcoating of components is performed prior to exposure, but even thenfrequent replacement of intricate components where salt water may betrapped is necessary.

One particular application that has proven difficult to properlymaintain is the sealing systems found on watertight doors used onseagoing vessels. The seals are contained within a channel formed from alip of the door and a weldment to contain the seal. This constructionprovides various crevices in which protective coatings are difficult toapply and in which seawater tends to collect in use leading to rapidcorrosion of the seal system and failure of the door.

It is known to apply coatings through the use of fluidized beds tocomponents as shown for example in U.S. Pat. No. 6,444,032. The coatingof a door assembly with a seal retention system does however posefurther challenges, in particular because of the intricate nature of theseal retention system.

It is therefore an object of the present invention to obviate ormitigate the disadvantages found in prior systems.

SUMMARY OF THE INVENTION

According to the present invention there is provided a method ofapplying a coating to a component which comprises steps of positioningsaid component adjacent to a fluidized bed, immersing the component intothe fluidized bed to apply a coating thereto, moving the componentwithin the fluidized bed during application of the coating, removing thecomponent from the fluidized bed.

DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of exampleonly with reference to the accompanying drawings in which

FIG. 1 is a schematic representation of a process flow for coating acomponent.

FIG. 2 is a perspective view of a transfer and coating apparatus shownin FIG. 1.

FIG. 3 is an enlarged perspective view of a portion of the apparatusshown in FIG. 2.

FIG. 4 is a view on the line IV-IV of FIG. 3.

FIG. 5 is a front view of the apparatus shown in FIG. 4.

FIG. 6 is a top view of the apparatus shown in FIG. 4,

FIG. 7 is a view similar to FIG. 1 of an alternative process,

FIG. 8 is a perspective view of a component to be coated by the processof FIG. 1 or 7.

FIG. 9 is a section on the line IX-IX of FIG. 8.

FIG. 10 is a flow chart showing a sequence of steps performed inreconditioning a component.

FIG. 11 is a view similar to FIG. 8 of another embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring firstly to FIG. 8, a component 10 that is to be coated is inthe form of a door having an outer surface 12, and a frame 14. On theframe 14 there is provided a seal retainer 18 that carries a sealassembly (not shown) and cooperates with a door frame. The seal retainer18 is formed as a channel in which a seal sits and has an overturned lipand a flange welded to the frame 14 to define the channel. The channelis of convoluted configuration and is therefore difficult to coat in amanner that fills the voids between the retainer 18 and the frame 14. Itwill be appreciated that the door is merely exemplary of the componentsthat may be coated and is itself of known construction.

Referring to FIG. 1, a coating process for the component 10 is shown inwhich the component 10 is moved between different stations by anoverhead conveyor indicated at 20. The conveyor 20 is a conventionalchain conveyor with hangers that allow components to be suspended fromthe conveyor. The hanger is shown in FIG. 8 and has a body 22 with apair of hooks 24 extending upwardly for engagement with the conveyor 20.The body 22 has central aperture 26 with a series of lower hooks 28extending below a lower edge 30 of the body 22. The lower hooks 28 haveupturned ends to engage a lip on the upper edge of the frame 14. Theexact form of the hangers 22 will vary depending upon the nature of thecomponent 10 but, as is standard practice, seek to minimise thefootprint of the suspension system on the component 10.

Referring again to FIG. 1, the conveyor 20 moves the component 12through an oven 40 to a transfer station 42. At the transfer station 42the component 10 is transferred onto a lateral conveyor 44, to bedescribed in more detail below so that it may be transferred intoalignment with a fluidized bed or fluid bed 46. The lateral conveyor 44positions the component within the fluidized bed for a predeterminedtime and then retracts the component and transfers it to an air blow offstation 48. The purpose of the air blow off station is to remove surpluscoating deposited by the fluidized bed. The component 10 is thentransferred by the conveyor 44 back to the conveyor 20 which moves thecomponent through an electrostatic coating station 50. A further coatingis applied at coating station 50 to that applied in the fluidized bedand the conveyor carries the component through into a curing oven 52.

The lateral conveyor 42 can best be seen in FIG. 2 and comprises a pairof support rails 60 that extend between the transfer station 42 and thecuring station 52. The support rails 60 carry a pair of tracks 62 onrollers 64 so that the tracks 62 can move along the rails 60 in unisonas indicated by arrow A. A turntable 66 is mounted on the track 62through rollers 68 that allow the carriage 66 to move along the axis ofthe tracks 62 as indicated by arrow B. The combination of the rails 60and track 62 allow the carriage to move in orthogonal axes forpositioning relative to the various stations involved in the processingof the component.

A mast 70 is rotatably coupled to the turntable 66 and comprises a pairof spaced columns 72 that have a channel cross section. The mast 70supports a carriage assembly 74 for movement along the axis of thecolumns 72 as indicated by the arrow C. The carriage assembly 74 has ahook 76 that has a distal end arranged to engage the aperture 26 in thehanger 22.

Referring to the mast 70 in more detail in FIGS. 3 to 6, the columns 72provide guides for wheels 80. The wheels 80 are rotatably supported uponarms 82 disposed at opposite sides of a base plate 84. A housing 86 issecured to the base plate 84 and has a pair of oppositely directedguides 88 disposed parallel to the channels 72. The hook assembly 76 isslidably mounted within the guides 88 by wheels 91.

An air cylinder 92 is connected between the hook assembly 76 and thebase plate 84 and may extend and retract along an axis parallel to theguides 88. A hose 94 supplies pressurised air to the cylinder 92. Thehose 94 is connected to a compressor 95 through a valve 96 that can openand close repeatedly through solenoid 98.

Hook 76 extends perpendicular to the base plate 84 and has a downwardlydepending body 97 that terminates with an outwardly extending foot 100.A notch 102 is formed on the upper surface of the foot 100 forengagement with the aperture 26 in the bracket 22.

A hoist 110 is located at the upper end of the mast 70 and is operableto raise or lower the carriage 74 through a chain 112. To reduce theload on the chain 112, the carriage 74 is counter balanced by a mass 114that slides within a tube 116 secured to the outside of one of thechannels 72. A cable 118 is connected between the mast 114 and the baseplate 84 by entrainment about a pulley 120. The mass 114 is chosen to beslightly less than the mass of the carriage 74 so that a tension ismaintained in the chain 112.

The transverse conveyor 44 is used to transfer the components 10 to thefluidized bed 46. This is performed by engaging the notch 100 within thewindow 26 of the bracket 22 and operating the hoist to lift the bracketoff the conveyor 20. The mast 70 is then moved laterally causing thetracks 62 to move along the rails 60 until the component 10 is alignedwith the opening in the fluidized bed 46. The mast 70 is then advancedalong the tracks 62 to position the component over the fluidized bed.The carriage 74 may then be lowered allowing the component 10 to becomesubmerged in the fluidized bed of coating material.

To facilitate the uniform and through coating of the component, theactuator 92 is pulsed to oscillate the component 10 along a verticalaxis within the fluidized bed and promote the uniform distribution ofthe coating material over the exterior surface of the component 10. Thepulsing of the component 10 provides a cyclic bodily translation of thecomponent within the fluidized bed that distributes the powder of thefluidized bed within the channel and at the same time prevents bridgingthe powder around the channel. An abrupt change of direction, ordeceleration is preferred, that may be effected through the control ofthe solenoid 98. It has been found that a pulse rate of between 5 pulsesper second and 0.5 pulses per second has provided satisfactory results.A pulse rate in the order of 2 pulses per second is preferred. In oneembodiment, the component 10 is a door nominally 66″ high by 26″ widethat weighs in the order of 100 lbs. Vertical amplitude of between 1″and 4″ has been attained.

After a designated time, typically in the order of 3 to 5 seconds, thecomponent is lifted from the bed 46 and the mast 70 moved rearwardlyalong the track 62 away from the bed. Thereafter the surplus materialcan be removed from the component 10 at the station 45 and the componentreturned to the conveyor 20 where it can be reattached to the conveyorand the hook assembly 76 released.

With certain coatings, the flow of the coating over the surface of thecomponent 10 can be promoted by vibrating the bracket 26 or hookassembly 76, which is transmitted in to the component. This iscomplementary to the translation of the component by the cylinder 92.

In an alternative process as shown in FIG. 7, a pair of fluidized beds46(a), 46(b) are arranged side by side. Each bed 46(a)(b) has a separatecoating component and the component may be initially immersed in thefirst bed, removed and transferred to the second bed through theoperation of the tracks 62 and the rails 60 where the component 10 isagain immersed. Thereafter, the component 10 can be positioned at theair blow off station 48 and returned to the conveyor for curing. In thisarrangement, electrostatic coating is not performed but rather a doublecoating is applied to the component. Oscillation of the componentthrough cylinder 92 may be performed at only the first step or at eachstep.

After curing, the component may be removed from the conveyor and thecontact points with the hooks covered with coating material. It willhowever be noted that the contact points are on an upper edge of thesurface of the component such that they would not be subjected to thesame corrosive environment as on the lower edges where water mayaccumulate.

It has been found in practice that the provision of dipping of thecomponent within the fluidized bed or beds enables a thorough coating tobe provided on the retainer 18 and to ensure that all surfaces arecoated to inhibit corrosion. The oscillation of the component whilstimmersed inhibits bridging of the coating with the intricatedconfiguration of the retainer 18 to ensure the surface is coated.

The hook assembly is mounted for movement independent of the mast,allowing the mast to perform the necessary translation and position withthe hook providing the oscillation. Other forms of oscillation can beutilised, such as a mechanical cam drive or hydraulic drive. Thefrequency of oscillation and the vertical excursion will vary accordingto the component being coated. The oscillation should be of sufficientamplitude and frequency to inhibit bridging of the powder coatingwithout removal of the component from the fluidized bed. Abrupt changesof direction are also preferred at the limits of the vertical movement.

The process of refurbishing a door that has been subject to corrosion isshown in FIG. 10. Initially the door is stripped of all mechanicalcomponents and the surface of the door blasted to remove corrosion. Thedoor is immersed in a neutralising agent to deactivate the corrosion andholes and other defects are repaired.

All sharp edges are then deburred to ensure there are no edges thatwould prevent proper coating. The door is then blasted to removecontaminants and phosphated to provide a base coat. The door is thenpassed in to the oven 40 to be heated in preparation for immersion inthe fluid bed 46. The first coating of epoxy is applied in the firstbed, using the actuator 92 to agitate the door within the bed and ensurefull encapsulation. The door is transferred to the second bed 46 b whereit is immersed in a polyester coating that offers high durability. Aftercoating and curing the door is inspected and tested for fit, includingthe dimensions of the seal channel.

The primary coating applied in the fluid bed is preferably a fusion bondpowder epoxy, such as grey zinc rich epoxy powder. The zinc content ofthe epoxy is preferably around sixty to-seventy percent by weight, whichprovides for resistance to undercreepage of the coating layer incorrosive environments. The presence of zinc in the coating also acts asa sacrificial element during the corrosion process. The secondarycoating applied in the fluid bed 46 b is a solid colour UV protectantlayer for the zinc epoxy, such as Protec Z series polyester sold byProtec Chemicals, Montreal Canada. Other suitable coating mediums may beused in fluidized beds such as nylon, PVCS, polyolefins, andpolyurethane.

A further embodiment is shown in FIG. 11 in which movement of the doorwithin the bed is used to inhibit bridging of the coating. In theembodiment of FIG. 10, like reference numerals are used to denote likecomponents with a suffix “a” added for clarity.

The bracket 22 a has a pair of arms 28 a that extend to either side ofthe door 10 a. The arms 28 a clamp to the midpoint of the door 10 athrough clamps 120 that can rotate relative to the arms 28 a. A chaindrive 122 is provided for one of the clamps 120 so that the door 10 acan be rotated about a horizontal axis when immersed. The rotation maybe continuous in one direction, may rotate a number of revolutions inone direction and the reverse, or may oscillate over partialrevolutions. The bodily movement of the door 10 a within the fluidizedbed is sufficient to inhibit bridging of the powder coating and therebyensure a cohesive coating of the door 10 a.

What is claimed is:
 1. A coating apparatus for coating a componentcomprising a fluidized bed of coating material, a conveyor to position acomponent above said fluidized bed, the conveyor including a mastmoveable relative to the fluidized bed, a carriage mounted on andmoveable vertically relative to said conveyor along the mast to lowersaid component into said fluidized bed, a hook assembly on said carriageto engage and carry said component, a drive acting on the hook assemblyto independently move said hook assembly vertically relative to saidcarriage and a control to periodically reverse the direction of movementof said hook assembly relative to said carriage to cause cyclic bodilymovement of said component in a vertical direction within said fluidizedbed as coating is applied, said drive applying periodic pulses to saidhook and thereby provide an abrupt change of direction of said hook in avertical direction relative to said carriage to promote a uniformdistribution of coating to an exterior surface of said component.
 2. Theapparatus of claim 1 wherein said drive includes an extendable cylinderacting between said hook assembly and said carriage.
 3. The apparatus ofclaim 2 wherein said hook assembly is slidably connected to saidcarriage and said extendible cylinder acts between said carriage andsaid hook assembly.
 4. The apparatus of claim 3 wherein a hoist ismounted on said mast and operates on said carriage to move said carriagealong said mast.
 5. The apparatus of claim 1 wherein a counterbalance isprovided for said carriage.
 6. The apparatus of claim 1 wherein saidmast is rotatably secured to said conveyor.
 7. The apparatus of claim 1wherein a plurality of fluidized beds are provided to coat saidcomponent and said conveyor extends between said beds.
 8. The apparatusof claim 7 wherein a material removal station is provided adjacent oneof said fluidized beds.
 9. The apparatus of claim 1 wherein said driveprovides a vertical displacement of between 1 inch and 4 inches.
 10. Theapparatus of claim 1 including an oven to heat said component prior totransfer by said conveyor to said fluidized bed.
 11. The apparatus ofclaim 10 wherein said mast depends from said conveyor and said mast isand rotatably secured to said conveyor to facilitate positioning of saidcomponent relative to said fluidized bed.
 12. A method of applying acoating to a component, including the steps of providing the apparatusof claim 11 to support said component, moving the mast along theconveyor to position said component above said fluidized bed of coatingmaterial, moving the hook assembly along the mast relative to theconveyor to lower the component into said fluidized bed to apply saidcoating thereto, operating the drive to apply pulses to the hookassembly to move the hook assembly vertically relative to the carriageand displace said component vertically relative to the carriage,periodically reversing the direction of movement of said hook assemblyrelative to the carriage to produce cyclic bodily translation of saidcomponent in a vertical direction within said fluidized bed duringapplication of said coating, the application of said pulses producing anabrupt change of direction of movement in a vertical direction relativeto said carriage to promote a uniform distribution of coating to anexterior surface of said component and lifting the hook assemblyrelative to the mast to remove the component from said fluidized bed.13. The method of claim 12 wherein said cyclic bodily translation has aperiod of between 5 cycles per second and 0.5 cycles per second.
 14. Themethod of claim 13 wherein said cyclic bodily translation has a periodof 2 cycles per second.
 15. The method of claim 12 wherein a pluralityof fluidized beds are provided and said component is moved successivelythrough said beds to apply a plurality of coatings thereto.
 16. Themethod of claim 12 wherein excessive coating material is removed uponremoval of said component from said fluidized bed.
 17. The method ofclaim 12 wherein said coating is fusion bond powder epoxy.
 18. Themethod of claim 1 wherein said component is subjected to vibrationduring bodily translation thereof.
 19. The method of claim 12 whereinsaid cyclic bodily translation has an amplitude of between 1 inch and 4inches.
 20. The method of claim 1 wherein said component is heated priorto immersion in said fluidized bed.
 21. The method of claim 1 whereinsaid component remains in said fluidized bed for a period of between 3and 5 seconds.